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“Wastewater Generation,
Characterization and
Conception of Wastewater
Treatment Plant”
Summer School on Wastewater Treatment
Plants and Management
Eugenio Foresti

Water Pollution
Water Pollution Alterations of water quality
due to discharge of wastes from point or diffuse
sources.
Wastewater Treatment
Water Pollution controll Treatment of wastes at
the source.
New Trend Biorefineries

Water Pollution
Main pollutants:
Organic carbon
Nitrogen compounds
Sulfur Compounds
Heavy metals
Microorganisms (contamination)

Water Pollution: Role of
Carbon, Nitrogen, Phosphorus and Sulphur
Compounds
Carbon:
Organic carbon compounds source of carbon and energy
for heterotrophic microorganisms. They catalize oxidation-
reduction reactions involving organic carbon compounds as source
of carbon and energy for growth and maintenance. Organic matter
decomposition in water bodies causes pollution.
Inorganic carbon (CO2) carbon source for growth of
autotrophic microorganisms that use sunlight or mediate oxidation-
reduction reactions envolving inorganic compounds as energy
source (e.g. NH4
+, S0, HS-, Fe3+...)

Compounds
Nitrogen (N) essential nutrient for cellular synthesis of amino
acids by microrganisms. In nature, N2 is sinthetized by green plants,
released as ammonia nitrogen by degradation of nitrogen containing
organic matter, and oxidized by autotrophic processes.
Phosphorus (P) essential nutrient for microorganisms synthesis
and maintenance (energy transfer - ATP/ADP system). In water
bodies, P is found as phosphate and it is the main responsible for
eutrophication.
Sulphur (S) present in many compounds used in industries and
as organic sulphur. In the aquatic environment S is found as oxidized
compounds (e.g. sulfate) or reduced compounds (e.g. sulfide).

Compounds
Changes of the oxidation state of Carbon, Nitrogen and
Sulphur occurring in water bodies:
- depletion of dissolved oxygen
- formation of indesirable products
- formation of inert products

Carbon, Nitrogen, Phosphorus and
Sulphur Compounds
Organic Matter (OM) Decomposition
Aerobic Environment
Heterotrophic microorganisms consume dissolved oxygen while
transform OM into CO2, H2O and new cells. Aquatic
environment become not viable for superior forms of life (e.g.
fish).
Anaerobic Environment
OM is not completely oxidized. Reduced organic compounds
can be released. Methane and other organic compounds are
formed.

8
Compounds
Nitrogen (N) Organic nitrogen (ON) is a constituent of
organic matter. ON is first converted to ammonia nitrogen (AN -
NH3, NH4
+). After, under aerobic condition, ammonia nitrogen is
sequencially converted to nitrite and nitrate. Nitrogen removal
occurs when nitrogen oxidized compounds (Nox) are biologically
converted to N2.
Phosphorus (P) organic P is liberated as phosphate.
Phosphate can be removed from the liquid phase by chemical
precipitation or as phosphate-rich biological sludge.
N and P micro-nutrients responsible for eutrophication
of lakes and reservoirs.

Carbon, Nitrogen, Phosphorus and
Sulphur Compounds
Organic and Inorganic Sulphur compounds (S)
some proteins have S in their composition and most wastewater
contain oxidized sulphur compounds. All sulfur compounds are
converted to sulfate under aerobic conditions. Sulfide is produced
under anaerobic conditions from organic matter decomposition and
sulfate biochemical reduction.

Main Characteristics of Wastewater of Interest
for Designing WTP
Roughly wastewaters can be classified as:
 Predominantly organic – Biological treatment is easily
applicable for removing OM.
 Predominantly inorganic – Physical-chemical treatment may
be applicable.
 Predominantly organic but containing toxic or recalcitrant
compounds – Biological treatment may be possible after
removing indesirable compounds.
Knowledge of the main characteristics of the wastewater:
very important for designing a proper WTP.

for Designing WTP
11
Organic Matter How to access
 Chemical Oxygen Demand – COD
 Biochemical Oxygen Demand – BOD
 Total Organic Carbon – TOC

for Designing WTP
TOTAL COD
COD B COD NB
COD RB COD SB COD PNB COD SNB
COMPLEX VFA COLOIDAL PARTICULATE
B – biodegradable; NB – nonbiodegradable; RB – readly biodegradable;
SB – slowly biodegradable; PNB – nonbiodegradable (particulate);
SNB – nonbiodegradable (soluble) VFA – Volatile Fatty Acids
COD Fractionation

for Designing WTP
13
Solids – How to access
Total Solids (TS) – residue remaining after evaporation and
drying of wastewater sample in stove (103 to 105oC)
Volatile Solids (VS) – solids that can be volatilized and burned
off when the TS are incinerated (500±50 oC)
Suspended Solids (SS) – portion of TS retained on a glass fiber
filter (pore size ~ 1.5 µm)
Dissolved Solids (DS) – solids that passes through the filter

for Designing WTP
Solids in Wastewater - Fractionation
 Total Volatile Solids (TVS)
1. Suspended Volatile Solids (SSV)
2. Dissolved Volatile Solids (DVS)
TVS = SSV + DSV
 Total Fixed Solids (TFS)
1. Suspended Fixed Solids – (SFS)
2. Dissolved Fixed Solids – (DFS)
TFS = SFS + DFS

Nitrogen in Wastewater – How to access
Nitrogen Fractionation
 Organic Nitrogen
 Ammonia Nitrogen
 Nitrite
 Nitrate
NTK

TKN
Ammonia N Organic N
Biodegradable Nonbiodegradable
Soluble Particulate Soluble Particulate
TKN – 60 – 70% as NH4
+
Nonbiodegradable N ~ 6% of SSV expressed as COD
Nitrogen fractionatin

Sulphur
 Sulfates and other sulphur oxidized compounds –
important because are reduced to sulfide under
anaerobic conditions
 Sulfides – may cause toxicity to biomas in biological
process; if in the gas phase - odor and corrosion
 Elemental Sulphur – may be formed in micro-aerobic
aquatic environment

pH – biological wastewater treatment are better conducted at pH
close to neutrality (6.6 to 7.8).
pH is one of the environmental factor thet selects the
microorganisms population. As far from the optimum range,
as selective the environment becomes.
Temperature – optimum ranges
psicrophylic (12 - 18 oC)
mesophylic (25 - 40 oC)
thermophylic (55 – 65 oC)
Temperature also selects the biomass; as far from the
optimum range, as selective the environment becomes.

Alkalinity – important as pH buffer
Due to the presence of hydroxides, carbonates and
bicarbonates.
In the pH range of interest – bicarbonate alkalinity
predominates
Bicarbonate Alkalinity (BA) – (HCO3
-) – very important for
pH controll of anaerobic processes and also as
carbon source in autotrophic biological processes

20
Oils and Grease (O&G) - high O&G (fatty compounds) may l
ead biological process to colapse. Normally O&G is
separated before the biological treatment units
Seattleable Solids (SeS) – inform on the volume occupied by
suspended solids that seattle after 60 min in Imhoff
flask
Heavy metals – possible toxicity

21
Pathogens
Bacteria – evaluated by the MPN (Most Probable Number) of
E. Coli (fecal coliform); E. Coli is not a pathogenic
microorganism. It is just an indicator of fecal contamination
Protozoa – evaluated for specific organisms (Cryptosporidium
parvum - oocysts, Entamoeba histolytica – cysts, Giardia
lambria – cysts)
Helminths – evaluated by counting eggs.

Interrelationships of Constituents
BOD/COD > 0.5 - wastewater easily treated by
biological processes.
0.3 < BOD/COD < 0.5 - biological treatment possible;
probable presence of inhibitors; need for biomass
acclimatization
BOD/COD < 0.3 – biological treatment difficult without pre-
treatment

Interrelationships of Interest Between
Some Wastewater Constituents
FS/VS – high values indicate predominance of inert matter
DFS/DVS – high values indicate high salinity
VSS/FSS – low values indicate high stabilized SS
Other information of interest:
Raw samples – FSS concentration can be associated to the
amount of grit in the influent
COD = 1.42 VSS

Flow Equalization
Flow equalization – becomes necessary when
variations in flow over time can impair the functioning
of the treatment units
Units: storage tank and pumping facilities.
Procedure to obtain the storage tank volume and the
equalized flow

Flow Equalization
V = 70 m3
Q = 13.55 m3.h-1
m3
h

Homogenization
Homogenization: Required when changes in
composition of the wastewater are very significant,
that it could cause instability in the processes
(chemical or biological) treatment.
There is no suitable method to obtain the
homogenization tank volume.

Homogenization
Industrial wastewater:
 Verify the possibility to hold effluents from
operations that occur sporadically throughout the
day in separated tanks. The effluents from these
tanks are released throughout the day.
 Verify the convenience of treating the segregated
effluents separately or mixing them before
treatment. The best option should be chosen
according to the characteristics of the final
effluent. .

The Treatment System as a Sequence of Phase
Separation and Conversion Process Units
Steps and Correspondig Objetives
1. Preliminary Treatment – Removal of grit and
coarse material in suspension – Protection of
equipment and facilities. The separated wastes go
to landifill.
2. Primary Treatment – Removal and stabilization of
settleable solids and fats (oils and greases).
Generates stabilized sludge. Further treatment is
necessary to eliminate microorganisms and
transform stabilized sludge in biosolids.

Steps and Objectives – cont.
3. Secondary Treatment – Removal of biodegradable
organic matter. Generates biological sludge to be
stabilized and properly disposed off.
4. Tertiary Treatment – Removal of nutrients (N, P).
Generates small amount of biological sludge. May
generate phosphate-rich sludge.
5. Advanced Treatment – Polishing of effluent for
reuse. Generates by products with high salt
concentration.

Steps and Objectives – cont.
5. Advanced Treatment – Polishing of effluent for
reuse. Generates byproducts with high concentration
of salts.
Steps 1 to 5 – removal of organic matter and some
specific compounds (N, P and salts).
Desinfection is an important step before discharging
contaminated wastewater in water bodies.

Phase Separation Units:
 Screen – coarse material
 Grit Chamber – grit
 Primary Settler – setteable solids; oil and grease
 Secondary Settler – biological sludge
Thickening Sludge Unit – pre-settled biological sludge

Phase Separation Units: cont.
 Flotation Unit – suspended solids
Dewatering Units (centrifuge, filter press, vacuum filter, etc.) –
biological or chemical sludge
 Membrane Units (ultrafiltration, microfiltration, reverse
osmosis) – very small particles, molecules

Conversion Process Units:
 Biological Reactors
 Aerobic Reactors – organic matter, nitrogen and sulphur
reduced compounds
Anaerobic Reactors – organic matter, nitrogen and
sulphur oxidized compounds
Anoxic Reators – nitrogen oxidized compounds
 Anaerobic Ponds
 Photosynthetic Ponds

Conversion Process Units: cont.
 Phisycal-Chemical Reactors
 Flocculation Unit – suspended solids
 Chemical precipitation Unit – metals
 Desinfection Unit - microorganisms

Typical Activated Sludge WTP – Franca – SP – Brazil – Operated by SABESP
Sector 1 – screen, grit
chamber , pumping
Sector 2 – primary
sedimentation
Sector 3 – aeration
tanks
Sector 4 – secondary
sedimentation
Sector 5 – sludge
thickening
Sector 6 – sludge
anaerobic digestion
Sector 7 – sludge
dewatering

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